1. Field of the Invention
This invention relates to the synthesis of hydrocarbons from a methane source. A particular application of this invention is a method for converting natural gas to more readily transportable material using a methane conversion catalyst formed using a reducible metal oxide, a support of oxides of at least two metals, and an alkali metal.
2. Description of the Pertinent Art
A major source of methane is natural gas. Other sources of methane have been considered for fuel supply (e.g., the methane present in coal deposits or formed during mining operations). Relatively small amounts of methane are also produced in various petroleum processes.
The composition of natural gas at the wellhead varies, but the major hydrocarbon present is methane. For example, the methane content of natural gas may vary within the range of about 40 to about 95 volume percent. Other constituents of natural gas include ethane, propane, butane, pentane (and heavier hydrocarbons), hydrogen sulfide, carbon dioxide, helium, and nitrogen.
Natural gas is classified as dry or wet, depending upon the amount of condensable hydrocarbons contained in it. Condensable hydrocarbons generally comprise C.sub.3 + hydrocarbons, although some ethane may be included. Gas conditioning is required to alter the composition of wellhead gas; processing facilities usually being located in or near the production fields. Conventional processing of wellhead natural gas yields processed natural gas containing at least a major amount of methane.
Large-scale use of natural gas often requires a sophisticated and extensive pipeline system. Liquefaction has also been employed as a transportation means, but processes for liquefying, transporting and revaporizing natural gas are complex, energy intensive and require extensive safety precautions. Transport of natural gas has been a continuing problem in the exploitation of natural gas resources. It would be extremely valuable to be able to convert methane (e.g., natural gas) to more readily transportable products. Moreover, direct conversion to olefins such as ethylene or propylene would be extremely valuable to the chemical industry.
Recently, it has been discovered that methane may be converted to higher hydrocarbons by a process which comprises contacting methane with an oxidative synthesizing agent at synthesizing conditions (e.g., at a temperature selected within the range of about 500.degree. to about 1000.degree. C.). An oxidative synthesizing agent is a composition having as a principal component at least one oxide of at least one metal, which composition produces higher C.sub.2 + hydrocarbon products, water and a composition comprising a reduced metal oxide when contacted with methane at synthesizing conditions. Reducible oxides of several metals have been identified which are capable of converting methane to higher hydrocarbons. In particular, oxides of manganese, tin, indium, germanium, lead, antimony and bismuth are most useful.
The reaction products of such processes are mainly ethylene, ethane, other light hydrocarbons, carbon oxides, coke and water. It would be beneficial to these oxidative synthesis processes to reduce production of carbon oxides and coke.
Accordingly, an object of this invention is to provide an improved process for converting methane to higher hydrocarbons. A further object of this invention is an improved oxidative synthesizing agent----one capable of converting methane with reduced byproduct selectivities.
Other aspects, objects and the several advantages of this invention will become apparent to those skilled in the art upon reading this Specification and the appended claims.